they tend to go pretty late. I got a notice for an interview in March, and interviewed in April, with the acceptance notice coming in a week before classes started. However, a classmate of mine was wait listed, never got in and a month after classes started for the year she was wait listed for the acceptance notice came in for the next year, without reapplying. Dont give up. Call every two weeks, keep them updated of any extra work you are doing- publication, abstracts, classes. Good luck!